I would stick to niche and small subreddits. Here is why.

1. Reddit has a lot of bots
2. Lots of real users are part of reddits contributor program which allows people to get paid from Reddit for their content. Theses users posts will get more visibility than the average lurker.
3. Reddit makes money off collecting data and selling it to advertisers. Reddit doesn't want quality community content and engagement. That is just what they promote to get people in the door. The more Reddit knows about their users, the more they can sell to advertisers. That is why they killed the third party apps for the most part. They are following the Facebook business model.

So basically if you're commenting on a a trending post that has 500+ comments, you're probably wasting your time by posting into the abyss. You might have bots and people downvoting your content so they can upvote their own content for more visibility.

Stick to the small subreddits if you're not trying to make money off Reddit and want a sense of an online community. It's not worth it to bots and community content creators to waste too much time in those communities.